NAME

mh-alias - alias file for nmh message system

SYNOPSIS

any nmh command

DESCRIPTION

This describes both nmh personal alias files and the global alias file
for nmh mail delivery, the file
/etc/nmh/MailAliases
It does not describe aliases files used by the message transport
system. Each line of the alias file has the format:
alias:address-group
or
alias;address-group
or
<alias-file
or
;comment
where:
address-group := address-list
| < file
| = UNIX-group
| + UNIX-group
| *
address-list := address
| address-list, address
Continuation lines in alias files end with `\' followed by the newline
character.
"Alias-file" and "file" are UNIX file names. UNIX-group is a group
name (or number) from /etc/group. An address is a "simple"
Internet-style address. Througout this file, case is ignored, except
for file names.
If the line starts with a `<', then the file named after the `<' is
read for more alias definitions. The reading is done recursively, so a
`<' may occur in the beginning of an alias file with the expected
results.
If the address-group starts with a `<', then the file named after the
`<' is read and its contents are added to the address-list for the
alias.
If the address-group starts with an `=', then the file /etc/group is
consulted for the UNIX-group named after the `='. Each login name
occurring as a member of the group is added to the address-list for the
alias.
In contrast, if the address-group starts with a `+', then the file
/etc/group is consulted to determine the group-id of the UNIX-group
named after the `+'. Each login name occurring in the /etc/passwd file
whose group-id is indicated by this group is added to the address-list
for the alias.
If the address-group is simply `*', then the file /etc/passwd is
consulted and all login names with a userid greater than some magic
number (usually 200) are added to the address-list for the alias.
In match, a trailing "*" on an alias will match just about anything
appropriate. (See example below.)
An approximation of the way aliases are resolved at posting time is
(it's not really done this way):
1) Build a list of all addresses from the message to be delivered,
eliminating duplicate addresses.
2) If this draft originated on the local host, then for those
addresses in the message that have no host specified, perform
alias resolution.
3) For each line in the alias file, compare "alias" against all of
the existing addresses. If a match, remove the matched "alias"
from the address list, and add each new address in the
address-group to the address list if it is not already on the
list. The alias itself is not usually output, rather the
address-group that the alias maps to is output instead. If
"alias" is terminated with a `;' instead of a `:', then both the
"alias" and the address are output in the correct format. (This
makes replies possible since nmh aliases and personal aliases are
unknown to the mail transport system.)
Since the alias file is read line by line, forward references work, but
backward references are not recognized, thus, there is no recursion.
Example Alias File:
</etc/nmh/BBoardAliases
sgroup: fred, fear, freida
b-people: Blind List: bill, betty;
fred: frated@UCI
UNIX-committee: <unix.aliases
staff: =staff
wheels: +wheel
everyone: *
news.*: news
The first line says that more aliases should immediately be read from
the file /etc/nmh/BBoardAliases. Following this, "fred" is defined as
an alias for "frated@UCI", and "sgroup" is defined as an alias for the
three names "frated@UCI", "fear", and "freida".
The alias "b-people" is a blind list which includes the addresses
"bill" and "betty"; the message will be delieved to those addresses,
but the message header will show only "Blind List: ;" (not the
addresses).
Next, the definition of "UNIX-committee" is given by reading the file
unix.aliases in the users nmh directory, "staff" is defined as all
users who are listed as members of the group "staff" in the /etc/group
file, and "wheels" is defined as all users whose group-id in
/etc/passwd is equivalent to the "wheel" group.
Finally, "everyone" is defined as all users with a user-id in
/etc/passwd greater than 200, and all aliases of the form
"news.<anything>" are defined to be "news".
The key thing to understand about aliasing in nmh is that aliases in
nmh alias files are expanded into the headers of messages posted. This
aliasing occurs first, at posting time, without the knowledge of the
message transport system. In contrast, once the message transport
system is given a message to deliver to a list of addresses, for each
address that appears to be local, a system-wide alias file is
consulted. These aliases are NOT expanded into the headers of messages
delivered.

HELPFULHINTS

To use aliasing in nmh quickly, do the following:
1) In your .mh_profile, choose a name for your alias file, say
"aliases", and add the line:
Aliasfile: aliases
2) Create the file "aliases" in your nmh directory.
3) Start adding aliases to your "aliases" file as appropriate.

FILES

/etc/nmh/MailAliases global nmh alias file

PROFILECOMPONENTS

Aliasfile: For a default alias file

SEEALSO

CONTEXT

None

BUGS

Although the forward-referencing semantics of mh-alias files prevent
recursion, the "< alias-file" command may defeat this. Since the
number of file descriptors is finite (and very limited), such infinite
recursion will terminate with a meaningless diagnostic when all the fds
are used up.
Forward references do not work correctly inside blind lists.